This invention relates to an optical fiber connector for connecting optical fibers together which are used as fiber-optic links in an optical communications system and a method of producing same.
An optical information transmitting system or optical communications system has been developed as a promising system that would take over the electrical information transmitting system now widely in use. In an optical communications system, pulses of light generated on the transmission side are transmitted down fibers of glass or optical fibers of a thickness of one hundred to several hundreds of .mu.m to the receiving side at which the pulses of light are converted into electric signals and taken out.
In this type of optical communications system, the most important problem is how to transmit information from the transmission side to the receiving side with a high degree of efficiency in a stable manner.
In the optical communications system, a loss of light would occur in the connections of optical fiber connectors for connecting together the optical fibers forming links and built into telephone trunk networks, for example, for transmitting signals. Advances made in the progress of the art have made it possible to reduce the loss occurring within the optical fibers to the range between a fraction of and 1 dB/km. In the optical fiber connectors, however, the loss that might occur has its size decided by the amount of eccentricity of the axes of a pair of optical fibers abutted against each other by an optical fiber connector. For example, in the case of an optical fiber of 125 .mu.m in diameter, if the axes of the optical fibers abutted against each other are off-center by about 4 .mu.m, a connection loss of about 0.5 dB would occur; if the eccentricity is about 7 .mu.m, the loss would be 1 dB.
Thus the present practice in transmitting information over a long distance by utilizing an optical communications system is to mount repeaters in the fiberoptic links at suitable intervals of space for amplifying signals that have been attenuated, before being transmitted to the destination. In this case, if the connection loss occurring in the optical fiber connectors is high, it would become necessary to increase the number of repeaters. An increase in the number of repeaters is not only undesirable from the economical point of view but also gives rise to many problems because it makes it necessary to perform maintenance and inspection more often and might reduce the reliability of the optical communications system as a whole.
The optical fibers may vary from one another in length depending on the locations at which they are installed or the channels through which information is transmitted. Thus the operation of attaching a connector to the terminal ends of the optical fibers has been required to be performed readily at the site of installation.
Accordingly the optical fiber connector should meet the requirements of low connection loss and easy assembly.
The optical fiber connector usually comprises a plug formed with a flange in an intermediate portion on its outer peripheral surface and a bore for containing an optical fiber in its center axial portion, a sleeve formed at its center axis with a through hole for fitting the outer peripheral surface of the plug and on its outer peripheral surface with threads, a cap nut adapted to threadably engage the thread generated in the sleeve, and a spring mounted between the plug and the cap nut for keeping constant the abutting force exerted by the plug. The accuracy in positioning an optical fiber owes largely to the accuracy in positioning the plug and sleeve relative to each other. In this respect, what is most important is how to minimize deviation of the axis of the plug from the axis of the optical fiber.
To this end, two types of plugs have hitherto been developed. One type has its outer case formed of hard metal which has a double eccentric cylinder built therein and the other type has a guide of jewels or ceramics embedded in the center axis and formed with a bore of a diameter slightly greater than that of the optical fiber.
In the plug of the type having the double eccentric cylinder, positioning of the optical fiber with respect to the center axis of the plug is effected by moving the two eccentric cylinders while making observations with a microscope after the optical fiber is fixed to the eccentric cylinders in the central portion of the plug. Thus this type has the disadvantage of being very poor in operability.
The plug having a guide embedded therein has the forward end of the optical fiber positioned by the guide, so that this type offers the advantage of the operability at the site of installation being greatly improved. However, working of the plug or aperturing the guide on the order of a fraction of millimeter would require highly advanced skills and a prolonged time for consummation, so that the operation would be very low in productivity.